Method for manufacturing magnetic recording medium and magnetic recording medium

ABSTRACT

A magnetic recording medium is presented that includes protruded magnetic patterns formed on a substrate, and a nonmagnetic material filled in recesses between the magnetic patterns in which an oxygen concentration thereof is higher at a surface side than at a substrate side. The nonmagnetic material is at least one selected from the group consisting of Si, SiC, SiC—C, SiOC, SiON, Si 3 N 4 , Al, Al x O y , Ti and TiO x .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/400,224, filed Mar. 9, 2009 now U.S. Pat. No. 8,043,516, which is aContinuation Application of PCT Application No. PCT/JP2008/061682, filedJun. 20, 2008, and for which priority is claimed under 35 U.S. C. §121and §120.

This application is based upon and claims the benefit of priority under35 U.S. C. §119 from Japanese Patent Application No. 2007-173047, filedJun. 29, 2007, the entire contents of all applications are incorporatedherein by reference in their entireties.

BACKGROUND

1. Field

One embodiment of the present invention relates to a method ofmanufacturing a magnetic recording medium, in particular a patternedmedium, and the magnetic recording medium manufactured by this method.

2. Description of the Related Art

In the information-oriented society in recent years, the amount ofinformation that needs to be stored in a recording medium has beencontinually increasing. To keep up with the increase in amount of data,there has been a demand for a recording medium and a recording apparatuswith a dramatically high recording density. As regards a hard disk forwhich there is an increasing demand as a high-capacity and inexpensivemagnetic recording medium, it is predicted that a recording density ofone terabits per square inch or more, which is about ten times higherthan the current recording density, will be required several yearsafter.

In an existing magnetic recording medium used in a hard disk, one bit isrecorded in a specific region of a thin film made of polycrystals offine magnetic grains. To raise the recording capacity of the magneticrecording medium, therefore, the recording density must be increased.For this purpose, a recording mark size usable in recording per bit mustbe reduced. If, however, the recording mark size is simply reduced,effect of recording noise caused by the shape of fine magnetic grainscannot be neglected. Instead, if the fine magnetic grains are furtherreduced in size, it is impossible to maintain the information recordedin fine magnetic grains at an ordinary temperature due to thermalfluctuation.

To avoid these problems, it is proposed to use a discrete bit-typepatterned medium in which recording dots are separated by a nonmagneticmaterial in advance so as to perform read and write using a singlerecording dot as one recording cell.

Also, in the magnetic recording medium incorporated into a hard diskdrive (HDD), there is an increasing problem of disturbance ofenhancement of track density due to interference between adjacenttracks. In particular, a serious technical subject is reduction of writeblurring due to fringe effect of magnetic fields from a write head. Tosolve such a problem, for example, a discrete track recording-typepatterned medium (DTR medium) has been proposed in which recordingtracks are physically separated. The DTR medium is capable of reducing aside erase phenomenon of erasing information of an adjacent track inwriting or a side read phenomenon of reading out information of anadjacent track in reading, and is capable of enhancing the trackdensity. Therefore, the DTR medium is expected as a magnetic recordingmedium capable of providing a high recording density. It should be notedthat the term “patterned medium” includes a discrete bit type patternedmedium and a DTR medium, in a broader sense.

To read and write a DTR medium with a flying head, it is desired toflatten the surface of the DTR medium. Specifically, in order to processa perpendicular magnetic recording layer with a thickness of 20 nm intoa patterned medium, grooves with a depth of 20 nm are formed. On theother hand, since the designed flying height of the flying head is about10 nm, the head may contact the patterned medium when deep grooves areleft behind. Accordingly, it has been attempted to fill the recessesbetween magnetic patterns with a nonmagnetic material so as to flattenthe medium surface.

In order to fill recesses between magnetic patterns and flatten thesurface, it has been known to deposit, for example, SiO or SiO₂ by RFsputtering (Jpn. Pat. Appln. KOKAI Publication No. 2006-236474).

However, since an oxygen-containing gas is used in the conventionalmethod for RF sputtering of the nonmagnetic material, there is a problemthe sidewalls of the magnetic patterns may be damaged by oxidation. Inaddition, process dusts may be produced or thickness dispersion of thenonmagnetic material may be caused by RF sputtering using theoxygen-containing gas.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A general architecture that implements the various feature of theinvention will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the invention and not to limit the scope of theinvention.

FIG. 1 is a plan view of a DTR medium according to an embodiment of theinvention along the circumferential direction;

FIG. 2 is a plan view of a discrete bit-type patterned medium accordingto another embodiment of the invention along the circumferentialdirection;

FIGS. 3A to 3H are cross-sectional views showing a method ofmanufacturing a patterned medium according to an embodiment of theinvention;

FIGS. 4A and 4B show the results of surface measurement of media with anatomic force microscope (AFM) after etch-back;

FIG. 5 shows the result of EDX analysis of compositional distribution inthe nonmagnetic material after etch-back; and

FIG. 6 is a cross-sectional view of the patterned medium having anonmagnetic material with compositional distribution.

DETAILED DESCRIPTION

Various embodiments according to the invention will be describedhereinafter with reference to the accompanying drawings. In general,according to one embodiment of the invention, there is provided a methodof manufacturing a magnetic recording medium, comprising: formingprotruded magnetic patterns on a substrate; depositing a nonmagneticmaterial in recesses between the magnetic patterns and on the magneticpatterns; and etching back the nonmagnetic material using anoxygen-containing etching gas while reforming a surface of thenonmagnetic material. According to another aspect of the presentinvention, there is provided a magnetic recording medium comprising:protruded magnetic patterns formed on a substrate; and a nonmagneticmaterial filled in recesses between the magnetic patterns, an oxygenconcentration thereof being higher at a surface side than at a substrateside.

FIG. 1 shows a plan view of a patterned medium (DTR medium) accordingtown embodiment of the invention along the circumferential direction. Asshown in FIG. 1, servo zones 2 and data zones 3 are alternately formedalong the circumferential direction of the patterned medium 1. The servozone 2 includes a preamble section 21, an address section 22 and a burstsection 23. The data zone 3 includes discrete tracks 31.

FIG. 2 shows a plan view of a patterned medium (discrete bit-typepatterned medium) according to another embodiment of the invention alongthe circumferential direction. Magnetic dots 32 are formed in the datazone 3 in this patterned medium.

A method of manufacturing a patterned medium according to an embodimentof the invention will be described with reference to FIGS. 3A to 3H.

On a glass substrate 51, a soft magnetic underlayer made of CoZrNb witha thickness of 120 nm, an underlayer for controlling orientation made ofRu with a thickness of 20 nm, a ferromagnetic layer 52 made ofCoCrPt—SiO₂ with a thickness of 20 nm and a protective layer 53 made ofcarbon (C) with a thickness of 4 nm are successively deposited. The softmagnetic underlayer and orientation control layer are not shown in thedrawing for simplification. Spin-on-glass (SOG) with a thickness of 100nm is spin-coated on the protective layer 53 as a resist 54. A stamper61 is disposed so as to face the resist 54. Patterns of protrusions andrecessed inverted to those of the magnetic patterns shown in FIG. 1 areformed on the stamper 61 (FIG. 3A).

Imprinting is performed by using the stamper 61 to form protrusions 54 aof the resist 54 corresponding to the recesses in the stamper 61 (FIG.2B).

Etching is performed with an ICP (inductively coupled plasma) etchingapparatus to remove resist residues remaining on the bottoms of therecesses of the patterned resist 54. The conditions in the process areas follows: for instance, CF₄ is used as the process gas, the chamberpressure is set to 2 mTorr, the coil RF power and the platen RF powerare set to 100 W, respectively, and the etching time is set to 30seconds (FIG. 2C).

Using the resist patterns (SOG) left unremoved as etching masks, ionmilling is performed with an ECR (electron cyclotron resonance) ion gunto etch the protective layer 53 with a thickness of 4 nm and theferromagnetic layer 52 with a thickness of 20 nm (FIG. 2D). Theconditions in the process are as follows: for instance, Ar is used asthe process gas, the microwave power is set to 800 W, the accelerationvoltage is set to 500V and the etching time is set to 3 minutes.

Then, the resist patterns (SOG) are stripped off with a RIE apparatus(FIG. 2E). The conditions in the process are as follows: for instance,CF₄ gas is used as the process gas, the chamber pressure is set to 100mTorr, the coil power is set to 400 W and the platen power is set to 100W.

Then, a SiC—C target (composition ratio: SiC 20%, C 80%) is mounted on asputtering apparatus, and a nonmagnetic material 55 is deposited in therecesses between the magnetic patters and on the magnetic pattern by DCsputtering (FIG. 3F). The conditions in the process are as follows: forinstance, an Ar flow rate is set to 80 sccm and a deposition time is setto 260 seconds. DC sputtering of a non-oxide target in a process gascontaining no oxygen prevents oxidative damage on the sidewalls of themagnetic patterns and suppresses process dusts.

Subsequently, the nonmagnetic material 55 is etched back (FIG. 3G). Theconditions in the process are as follows: for instance, an ECR ion gunis used, an Ar flow rate is set to 5 sccm and an O₂ flow rate is set to5 sccm, which are used as process gases, a microwave power is set to 800W, an acceleration voltage is set to 700V and an etching time is set toabout 6 minutes.

In the present invention, deposition of the nonmagnetic material 55shown in FIG. 3F and etch-back of the nonmagnetic material 55 shown inFIG. 3G may be repeated plural times.

Ar gas is used as the process gas in the etch-back process using theconventional ECR ion gun and ion-milling apparatus. On the contrary, anoxygen-containing gas, for example, a mixed gas of Ar and O₂ asdescribed above, is used as the process gas in the present invention.

FIGS. 4A and 4B show the results of surface measurement of the mediaafter the etch-back process with an atomic force microscope (AFM). AnAr—O₂ mixed gas is used in FIG. 4A, while Ar gas is used in FIG. 4B. Aswill be apparent from the comparison between FIGS. 4A and 4B, surfaceflatness at the same etch-back thickness is excellent in the case wherethe Ar—O₂ mixed gas is used over the case where Ar gas is used.

It is also found from the measurement with an optical surface analyzer(OSA) that thickness dispersion of the nonmagnetic material becomessmaller in the case where the Ar—O₂ mixed gas is used over the casewhere Ar gas is used.

The oxygen-containing gas may be used during the entire period of thetime for applying etch-back, or may be used during a part of the timeperiod. For example, when SiC—C with a thickness of 100 nm is depositedand then SiC—C is etched back by 100 nm, the oxygen-containing gas maybe used only for the time period for etching back the first 10 nm, orthe oxygen-containing gas may be used only for the time period foretching back the last 5 nm. Using the oxygen-containing gas at theinitial stage of etch-back is advantageous in view of flatness. Usingthe oxygen-containing gas at the final stage of etch-back isadvantageous in view of enhancement in shock-resistance of the mediumsince etching advances while the surface of the nonmagnetic material isreformed with O₂.

When deposition and etch-back of the nonmagnetic material are repeatedplural times, the oxygen-containing gas may be used, for example, at apart of the etch-back time in one etch-back step of plural etch-backsteps.

The oxygen concentration in the oxygen-containing gas is preferably from1 vol % or more to 70 vol % or less, more preferably from 5 vol % ormore to 70 vol % or less. If the oxygen concentration is less than 1 vol%, the surface reforming effect with oxygen is not exerted. The oxygenconcentration exceeding 70 vol % is not preferable since DLC and themagnetic material existing on the medium surface are damaged. The gaspressure as a sum of Ar and O₂ is preferably from 0.01 to 1.0 Pa. Theacceleration voltage for the beam is preferably in the range of 20 to1,000V.

One time each of deposition and etch-back of the nonmagnetic materialreduces the risk of dust generation since the process is simplified.Even when deposition and etch-back of the nonmagnetic material arerepeated plural times, throughput may be improved by providing pluraldeposition chambers and etch-back chambers, since the process time perone chamber may be shortened. It is preferable to repeat deposition andetch-back of the nonmagnetic material until the depth of the recesses asmeasured with an atomic force microscope (AFM) becomes 4 nm or less interms of flying characteristics of the head.

The end point of etch-back is judged at the time when Co contained inthe ferromagnetic layer is detected using a quadrupole mass spectrometer(Q-MASS).

Finally, carbon (C) is deposited by chemical vapor deposition (CVD) toform the protective layer 56 (FIG. 3H). Further, a lubricant is appliedto the protective layer 56 to provide a DTR medium.

Next, preferable materials to be used in the embodiments of the presentinvention will be described.

<Substrate>

As the substrate, for example, a glass substrate, Al-based alloysubstrate, ceramic substrate, carbon substrate or Si single crystalsubstrate having an oxide surface may be used. As the glass substrate,amorphous glass or crystallized glass is used. Examples of the amorphousglass include common soda lime glass and aluminosilicate glass. Examplesof the crystallized glass include lithium-based crystallized glass.Examples of the ceramic substrate include common aluminum oxide,aluminum nitride or a sintered body containing silicon nitride as amajor component and fiber-reinforced materials of these materials. Asthe substrate, those having a NiP layer on the above metal substrates ornonmetal substrates formed by plating or sputtering may be used.

<Soft Magnetic Underlayer>

The soft magnetic underlayer (SUL) serves a part of such a function of amagnetic head as to pass a recording magnetic field from a single-polehead for magnetizing a perpendicular magnetic recording layer in ahorizontal direction and to circulate the magnetic field to the side ofthe magnetic head, and applies a sharp and sufficient perpendicularmagnetic field to the recording layer, thereby improving read/writeefficiency. For the soft magnetic underlayer, a material containing Fe,Ni or Co may be used. Examples of such a material may include FeCo-basedalloys such as FeCo and FeCoV, FeNi-based alloys such as FeNi, FeNiMo,FeNiCr and FeNiSi, FeAl-based alloys and FeSi-based alloys such as FeAl,FeAlSi, FeAlSiCr, FeAlSiTiRu and FeAlO, FeTa-based alloys such as FeTa,FeTaC and FeTaN and FeZr-based alloys such as FeZrN. Materials having amicrocrystalline structure such as FeAlO, FeMgO, FeTaN and FeZrNcontaining Fe in an amount of 60 at % or more or a granular structure inwhich fine crystal grains are dispersed in a matrix may also be used. Asother materials to be used for the soft magnetic underlayer, Co alloyscontaining Co and at least one of Zr, Hf, Nb, Ta, Ti and Y may also beused. Such a Co alloy preferably contains 80 at % or more of Co. In thecase of such a Co alloy, an amorphous layer is easily formed when it isdeposited by sputtering. Because the amorphous soft magnetic material isnot provided with crystalline anisotropy, crystal defects and grainboundaries, it exhibits excellent soft magnetism and is capable ofreducing medium noise. Preferable examples of the amorphous softmagnetic material may include CoZr-, CoZrNb- and CoZrTa-based alloys.

An underlayer may further be formed beneath the soft magnetic underlayerto improve the crystallinity of the soft magnetic underlayer or toimprove the adhesion of the soft magnetic underlayer to the substrate.As the material of such an underlayer, Ti, Ta, W, Cr, Pt, alloyscontaining these metals or oxides or nitrides of these metals may beused. An intermediate layer made of a nonmagnetic material may be formedbetween the soft magnetic underlayer and the recording layer. Theintermediate layer has two functions including the function to cut theexchange coupling interaction between the soft magnetic underlayer andthe recording layer and the function to control the crystallinity of therecording layer. As the material for the intermediate layer Ru, Pt, Pd,W, Ti, Ta, Cr, Si, alloys containing these metals or oxides or nitridesof these metals may be used.

In order to prevent spike noise, the soft magnetic underlayer may bedivided into plural layers and Ru layers with a thickness of 0.5 to 1.5nm are interposed therebetween to attain anti-ferromagnetic coupling.Also, a soft magnetic layer may be exchange-coupled with a pinning layerof a hard magnetic film such as CoCrPt, SmCo or FePt having longitudinalanisotropy or an anti-ferromagnetic film such as IrMn and PtMn. Amagnetic film (such as Co) and a nonmagnetic film (such as Pt) may beprovided under and on the Ru layer to control exchange coupling force.

<Ferromagnetic Layer>

For the perpendicular magnetic recording layer, a material containing Coas a main component, at least Pt and further an oxide is preferablyused. The perpendicular magnetic recording layer may contain Cr ifneeded. As the oxide, silicon oxide or titanium oxide is particularlypreferable. The perpendicular magnetic recording layer preferably has astructure in which magnetic grains, i.e., crystal grains havingmagnetism, are dispersed in the layer. The magnetic grains preferablyhave a columnar structure which penetrates the perpendicular magneticrecording layer in the thickness direction. The formation of such astructure improves the orientation and crystallinity of the magneticgrains of the perpendicular magnetic recording layer, with the resultthat a signal-to-noise ratio (SN ratio) suitable to high-densityrecording can be provided. The amount of the oxide to be contained isimportant to provide such a structure.

The content of the oxide in the perpendicular magnetic recording layeris preferably 3 mol % or more and 12 mol % or less and more preferably 5mol % or more and 10 mol % or less based on the total amount of Co, Crand Pt. The reason why the content of the oxide in the perpendicularmagnetic recording layer is preferably in the above range is that, whenthe perpendicular magnetic recording layer is formed, the oxideprecipitates around the magnetic grains, and can separate fine magneticgrains. If the oxide content exceeds the above range, the oxide remainsin the magnetic grains and damages the orientation and crystallinity ofthe magnetic grains. Moreover, the oxide precipitates on the upper andlower parts of the magnetic grains, with an undesirable result that thecolumnar structure, in which the magnetic grains penetrate theperpendicular magnetic recording layer in the thickness direction, isnot formed. The oxide content less than the above range is undesirablebecause the fine magnetic grains are insufficiently separated, resultingin increased noise when information is reproduced, and therefore, asignal-to-noise ratio (SN ratio) suitable to high-density recording isnot provided.

The content of Cr in the perpendicular magnetic recording layer ispreferably 0 at % or more and 16 at % or less and more preferably 10 at% or more and 14 at % or less. The reason why the content of the Cr ispreferably in the above range is that the uniaxial crystal magneticanisotropic constant Ku of the magnetic grains is not too much reducedand high magnetization is retained, with the result that read/writecharacteristics suitable to high-density recording and sufficientthermal fluctuation characteristics are provided. The Cr contentexceeding the above range is undesirable because Ku of the magneticgrains is lowered, and therefore, the thermal fluctuationcharacteristics are deteriorated, and also, the crystallinity andorientation of the magnetic grains are impaired, resulting indeterioration in read/write characteristics.

The content of Pt in the perpendicular magnetic recording layer ispreferably 10 at % or more and 25 at % or less. The reason why thecontent of Pt is preferably in the above range is that the Ku valuerequired for the perpendicular magnetic layer is provided, and further,the crystallinity and orientation of the magnetic grains are improved,with the result that the thermal fluctuation characteristics andread/write characteristics suitable to high-density recording areprovided. The Pt content exceeding the above range is undesirablebecause a layer having an fcc structure is formed in the magnetic grainsand there is a risk that the crystallinity and orientation are impaired.The Pt content less than the above range is undesirable because a Kuvalue satisfactory for the thermal fluctuation characteristics suitableto high-density recording is not provided.

The perpendicular magnetic recording layer may contain one or more typesof elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru and Rebesides Co, Cr, Pt and the oxides. When the above elements arecontained, formation of fine magnetic grains is promoted or thecrystallinity and orientation can be improved and read/writecharacteristics and thermal fluctuation characteristics suitable tohigh-density recording can be provided. The total content of the aboveelements is preferably 8 at % or less. The content exceeding 8 at % isundesirable because phases other than the hcp phase are formed in themagnetic grains and the crystallinity and orientation of the magneticgrains are disturbed, with the result that read/write characteristicsand thermal fluctuation characteristics suitable to high-densityrecording are not provided.

As the perpendicular magnetic recording layer, a CoPt-based alloy,CoCr-based alloy, CoPtCr-based alloy, CoPtO, CoPtCrO, CoPtSi, CoPtCrSi,a multilayer structure of an alloy layer containing at least one typeselected from the group consisting of Pt, Pd, Rh and Ru and a Co layer,and materials obtained by adding Cr, B or O to these layers, forexample, CoCr/PtCr, CoB/PdB and CoO/RhO may be used.

The thickness of the perpendicular magnetic recording layer ispreferably 5 to 60 nm and more preferably 10 to 40 nm. When thethickness is in this range, a magnetic recording apparatus suitable tohigher recording density can be manufactured. If the thickness of theperpendicular magnetic recording layer is less than 5 nm, read outputsare too low and noise components tend to be higher. If the thickness ofthe perpendicular magnetic recording layer exceeds 40 nm, read outputsare too high and the waveform tends to be distorted. The coercivity ofthe perpendicular magnetic recording layer is preferably 237000 A/m(3000 Oe) or more. If the coercivity is less than 237000 A/m (3000 Oe),thermal fluctuation resistance tends to be deteriorated. Theperpendicular squareness of the perpendicular magnetic recording layeris preferably 0.8 or more. If the perpendicular squareness is less than0.8, the thermal fluctuation resistance tends to be deteriorated.

<Protective Layer>

The protective layer is provided for the purpose of preventing corrosionof the perpendicular magnetic recording layer and also preventing thesurface of a medium from being damaged when the magnetic head is broughtinto contact with the medium. Examples of the material of the protectivelayer include those containing C, SiO₂ or ZrO₂. The thickness of theprotective layer is preferably 1 to 10 nm. This is preferable forhigh-density recording because the distance between the head and themedium can be reduced. Carbon may be classified into sp²-bonded carbon(graphite) and sp³-bonded carbon (diamond). Though sp³-bonded carbon issuperior in durability and corrosion resistance to graphite, it isinferior in surface smoothness to graphite because it is crystallinematerial. Usually, carbon is deposited by sputtering using a graphitetarget. In this method, amorphous carbon in which sp²-bonded carbon andsp³-bonded carbon are mixed is formed. Carbon in which the ratio ofsp³-bonded carbon is larger is called diamond-like carbon (DLC). DLC issuperior in durability and corrosion resistance and also in surfacesmoothness because it is amorphous and therefore utilized as the surfaceprotective layer for magnetic recording media. The deposition of DLC byCVD (chemical vapor deposition) produces DLC through excitation anddecomposition of raw gas in plasma and chemical reactions, andtherefore, DLC richer in sp³-bonded carbon can be formed by adjustingthe conditions.

Next, preferred manufacturing conditions in each process in theembodiments of the present invention will be described.

<Imprinting>

A resist is applied to the surface of a substrate by spin-coating andthen, a stamper is pressed against the resist to thereby transfer thepatterns of the stamper to the resist. As the resist, for example, ageneral novolak-type photoresist or spin-on-glass (SOG) may be used. Thesurface of the stamper on which patterns of protrusions and recessescorresponding to servo information and recording tracks are formed ismade to face the resist on the substrate. In this process, the stamper,the substrate and a buffer layer are placed on the lower plate of a dieset and are sandwiched between the lower plate and the upper plate ofthe die set to be pressed under a pressure of 2000 bar for 60 seconds,for example. The height of the protrusions of the patterns formed on theresist by imprinting is, for instance, 60 to 70 nm. The above conditionsare kept for about 60 seconds for transporting the resist to beexcluded. In this case, if a fluorine-containing peeling agent isapplied to the stamper, the stamper can be peeled from the resistsatisfactorily.

<Removal of Resist Residues>

Resist residues left unremoved on the bottoms of the recesses of theresist are removed by RIE (reactive ion etching). In this process, anappropriate process gas corresponding to the material of the resist isused. As the plasma source, ICP (inductively coupled plasma) apparatuscapable of producing high-density plasma under a low pressure ispreferable, but an ECR (electron cyclotron resonance) plasma or generalparallel-plate RIE apparatus may be used.

<Etching of Ferromagnetic Layer>

After the resist residues are removed, the ferromagnetic layer isprocessed using the resist patterns as etching masks. For the processingof the ferromagnetic layer, etching using Ar ion beams (Ar ion milling)is preferable. The processing may be carried out by RIE using Cl gas ora mixture gas of CO and NH₃. In the case of RIE using the mixture gas ofCO and NH₃, a hard mask made of Ti, Ta or W is used as an etching mask.When RIE is used, a taper is scarcely formed on the side walls of theprotruded magnetic patterns. In processing the ferromagnetic layer by Arion milling capable of etching any material, if etching is carried outunder the conditions that, for example, the acceleration voltage is setto 400V and incident angle of ions is varied between 30° and 70°, ataper is scarcely formed on the side walls of the protruded magneticpatterns. In milling using an ECR ion gun, if etching is carried outunder static opposition arrangement (incident angle of ions is 90°), ataper is scarcely formed on the side walls of the protruded magneticpatterns.

<Stripping of Resist>

After the ferromagnetic layer is etched, the resist is stripped off.When a general photoresist is used as the resist, it can be easilystripped off by oxygen plasma treatment. Specifically, the photoresistis stripped off by using an oxygen ashing apparatus under the conditionsthat the chamber pressure is 1 Torr, power is 400 W and processing timeis 5 minutes. When SOG is used as the resist, SOG is stripped off by RIEusing fluorine-containing gas. As the fluorine-containing gas, CF₄ orSF₆ is suitable. Note that, it is preferable to carry out rinsing withwater because the fluorine-containing gas reacts with moisture in theatmosphere to produce an acid such as HF and H₂SO₄. Redeposited productsmay be rinsed with exposure to H₂ plasma of H₂O plasma.

<Deposition of Nonmagnetic Material>

After stripping of the resist, a nonmagnetic material is deposited inthe recesses between the magnetic patterns and on the magnetic patterns.In this step, the nonmagnetic material is deposited by bias sputteringor usual sputtering. The nonmagnetic material may be selected from Si,SiC, SiC—C, SiOC, SiON, Si₃N₄, Al, Al_(x)O_(y), Ti, TiO_(x) and amixture thereof. The bias sputtering is a method in which thenonmagnetic material is deposited by sputtering while a bias is appliedto the substrate and is capable of readily filling the recesses with thedeposited nonmagnetic material. However, since the bias to the substrateis liable to damage the substrate as well as to produce sputteringdusts, usual sputtering may be favorably used. DC sputtering is morepreferable than RF sputtering, although RF sputtering may be available,because the latter tends to cause thickness dispersion of thenonmagnetic material.

<Etch-Back of Nonmagnetic Material>

Etch-back of the nonmagnetic material is carried out until theferromagnetic film (or the carbon protective film on the ferromagneticfilm) is exposed. This etch-back process is preferably carried out byion milling. When a silicon-based nonmagnetic material such as SiO₂ isused, the nonmagnetic material may be etched back by RIE using afluorine-containing gas. Etching with an ECR ion gun is also available.When O₂ is added to the process gas as described above, etch-back can beperformed while reforming the surface of the nonmagnetic material. Toenhance planarization, etch-back is preferably performed in theperpendicular direction. In addition, deposition of nonmagnetic materialand etch-back thereof may be repeated plural times.

<Deposition of Protective Layer and Aftertreatment>

After etch-back, a carbon protective layer is deposited. The carbonprotective layer may be deposited by CVD, sputtering or vacuumevaporation. CVD produces a DLC film containing a large amount ofsp³-bonded carbon. A carbon protective layer with a thickness less than2 nm is not preferable because it results in unsatisfactory coverage. Acarbon protective layer with a thickness exceeding 10 nm is notpreferable because it increases magnetic spacing between a read/writehead and a medium, leading to deterioration in SNR. A lubricant isapplied to the surface of the protective layer. As the lubricant, forexample, perfluoropolyether, fluorinated alcohol, fluorinated carboxylicacid or the like is used.

EXAMPLES Example 1

Using a stamper having patterns of protrusions and recesses of servopatterns (preamble, address, and burst) and recording tracks formedthereon as shown in FIG. 1, a DTR medium was manufactured in the methodshown in FIGS. 3A to 3H. In the step of FIG. 3F, a nonmagnetic materialwas deposited by DC sputtering using a SiC—C target. Specifically, theAr flow rate was set to 80 sccm and the deposition time was set to 260seconds, and a SiC—C film with a thickness of 100 nm was deposited. Ananalysis of the surface of the nonmagnetic material by secondary ionmass spectrometry (SIMS) showed that Si content was 7.47 at %, O contentwas 5.51 at % and C content was 87.1 at %. In the step of FIG. 3G, thenonmagnetic material was etched back with an ECR ion gun. Thenonmagnetic material was etched back using a mixed gas of Ar and O₂ at amicrowave power of 800 W and an acceleration voltage of 700V for about12 minutes. FIG. 5 shows the results of EDX analysis for compositionaldistribution in the nonmagnetic material after the etch-back process. Asshown in the drawing, it was confirmed that the concentration of Odecreased while the concentration of C increased from the surface towardthe substrate.

FIG. 6 shows a cross-sectional view of a patterned medium having thenonmagnetic material with compositional distribution. A soft magneticlayer 72 is formed on a substrate 71, and protruded patterns offerromagnetic layer 73 and protective layer 74 made of carbon are formedon the soft magnetic layer 72. The nonmagnetic material is filled in therecesses between the protruded patterns of the ferromagnetic layer 73.This nonmagnetic material includes a substrate-side nonmagnetic material(SiC—C) 75 a and a surface-side nonmagnetic material (SiOC) 75 b.

A measurement of the land/groove ratio in the track region by MFM showedthat the ratio was 2:1 that is approximately equal to the ratio beforefilling with the nonmagnetic material. As a result of acoustic emission(AE) measurement using a glide head, no AE signal was observed.

Comparative Example 1

A patterned medium was manufactured by the conventional method using thesame stamper as in Example 1. In the step of FIG. 3F, RF sputteringusing a SiO target was performed at an Ar flow rate of 75 sccm and an O₂flow rate of 5 sccm, and a SiO₂ film with a thickness of 100 nm wasdeposited by setting the sputtering time to 500 seconds. The result ofSIMS analysis showed that the film was composed of SiO₂ (36.0 at %) andO (64.0 at %). In the step of FIG. 3G, the nonmagnetic material wasetched back with an ECR ion gun. The etch-back conditions were asfollows: Ar was used as a process gas, a microwave power was set to 800W and an acceleration voltage was set to 700V, and etch-back isperformed for about 15 minutes.

A measurement of the land/groove ratio in the track region by MFM showedthat the width of the land (ferromagnetic layer portion) was decreasedfrom that before filled with the nonmagnetic material, and the ratio wasabout 1:1. It was found that the land/groove ratio was varied due toprocess damage. As a result of acoustic emission (AE) measurement usinga glide head, AE signals were observed. This seems to be due to a largequantity of process dusts produced in RF sputtering.

The above results show that the method of Example 1 gives less damage tothe ferromagnetic layer as compared with the method of ComparativeExample 1, and a medium having good surface flatness (i.e., no AE signalis observed) may be manufactured by the method of Example 1.

Example 2

Using a stamper having patterns of protrusions and recesses of servopatterns (preamble, address, and burst) and recording tracks formedthereon as shown in FIG. 1, a DTR medium was manufactured in the methodshown in FIGS. 3A to 3H. In the step shown of FIG. 3F, a nonmagneticmaterial was deposited by DC sputtering using a SiC—C target.Specifically, the Ar flow rate was set to 80 sccm and the depositiontime was set to 260 seconds, and a SiC—C film with a thickness of 100 nmwas deposited. In the step of FIG. 3G, the nonmagnetic material wasetched back with an ECR ion gun. The nonmagnetic material was etchedback using a mixed gas of Ar and O₂ at a microwave power of 800 W and anacceleration voltage of 700V for about 12 minutes.

The thickness distribution of the filled nonmagnetic material wasmeasured using NANOSPEC (trade name; manufactured by Nanometrics). As aresult, almost no thickness distribution was observed in the medium, inwhich the difference of thickness between the thickest portion andthinnest portion was 1% of the thickness.

Comparative Example 2

A patterned medium was manufactured by the conventional method using thesame stamper as in Example 1. In the step of FIG. 3F, RF sputteringusing a SiO target was performed at an Ar flow rate of 75 sccm and an O₂flow rate of 5 sccm, and a SiO₂ film with a thickness of 100 nm wasdeposited by setting the sputtering time to 500 seconds. The result ofSIMS analysis showed that the film was composed of SiO₂ (36.0 at %) andO (64.0 at %). In the step of FIG. 3G, the nonmagnetic material wasetched back with an ECR ion gun. The etch-back conditions were asfollows: Ar was used as a process gas, a microwave power was set to 800W and an acceleration voltage was set to 700V, and etch-back isperformed for about 15 minutes.

The thickness distribution of the filled nonmagnetic material wasmeasured using NANOSPEC (trade name; manufactured by Nanometrics). As aresult, thickness distribution of the nonmagnetic material was observedbetween the upper and lower portions of the medium, in which differencein the thickness was 10% at maximum.

Comparison between Example 2 and Comparative Example 2 shows thefollowings. When the nonmagnetic material is deposited by RF sputteringusing an oxygen-containing gas as in Comparative Example 2, about 10% ofthickness dispersion may be caused. This corresponds to difference inlevel of 10 nm for the nonmagnetic material with a thickness of 100 nm.It is not preferable that the nonmagnetic material with a thickness of 4nm or more remains on the ferromagnetic layer in terms of magneticspacing. On the contrary, a medium with small thickness distribution canbe manufactured in Example 2.

Example 3

A DTR medium was manufactured by a similar method to that in Example 1,except that steps of depositing SiC—C with a thickness of 100 nm andetching-back SiC—C were repeated 5 times. The cross-sectional of the DTRmedium was observed with TEM. It was confirmed from the light and shadeof the TEM image that the nonmagnetic material filled in the recesses iscomprised of five layers. The compositional distribution of one layer ofthe nonmagnetic material was the same as in Example 1.

Since observation of a stacked structure of the nonmagnetic material wasimpossible in some medium, the composition was evaluated by SIMS. Asshown in FIG. 5, decrease in O concentration and increase in Cconcentration from the surface side toward the substrate side wereobserved.

Touchdown and takeoff test was carried out for the medium. A differencein pressure AP between touchdown and takeoff was 0.18 atm. After thetest, the surface of the medium was observed for bright spots due tofine dusts. As a result, no significant change was observed.

Comparative Example 3

A patterned medium was manufactured by the conventional method using thesame stamper as in Example 1. In the step of FIG. 3F, RF sputteringusing a SiO target was performed at an Ar flow rate of 75 sccm and an O₂flow rate of 5 sccm, and a SiO₂ film with a thickness of 100 nm wasdeposited by setting the sputtering time to 500 seconds. The result ofSIMS analysis showed that the film was composed of SiO₂ (36.0 at %) andO (64.0 at %). In the step of FIG. 3G, the nonmagnetic material wasetched back with an ECR ion gun. The etch-back conditions were asfollows: Ar was used as a process gas, a microwave power was set to 800W and an acceleration voltage was set to 700V, and etch-back isperformed for about 15 minutes. The sectional TEM observation revealedthat the recesses were filled with SiO₂ having uniform composition.

Touchdown and takeoff test was carried out for the medium. A differencein pressure AP between touchdown and takeoff was 0.05 atm. After thetest, the surface of the medium was observed for bright spots due tofine dusts. As a result, a large number of bright spots were produced.When the cross-section of the medium was observed with SEM, it was shownthat cracks were produced at portions where the head contacted.

Comparison between Example 3 and Comparative Example 3 shows thefollowings. When the nonmagnetic material used is SiO_(x) having highhardness as in Comparative Example 3, cracks are likely to be producedby application of impact, leading to dust generation. On the contrary,in Example 3, since the nonmagnetic material filled in the recesses hasa multilayered structure or composition distribution in which differencein density of the material is produced between the layers, impactapplied to the medium seems to be absorbed by the nonmagnetic material.

Example 4

A DTR medium was manufactured by the same method as in Example 1, exceptthat different kinds of nonmagnetic materials were used. The nonmagneticmaterials used were Si, SiC, SiOC, SiON, Si₃N₄, Al, Al_(x)O_(y), Ti andTiO_(x). These nonmagnetic materials were deposited by bias sputteringor DC sputtering. It was confirmed that no AE signal was observed in anyof the DTR media.

Comparative Example 4

A DTR medium was manufactured by the same method as in Example, exceptthat Cu was used as the nonmagnetic material. AE signals were observedin this DTR medium. This is because Cu was heated and ref lowed duringthe steps of sputtering and etch-back and the surface morphology of themedium was impaired.

A DTR medium was manufactured by the same method as in Example 1, exceptthat carbon (C) was used as the nonmagnetic material. AE signals werealso observed in this DTR medium. This is because the surface roughnessRa was increased due to reaction between carbon and oxygen.

Example 5

A nonmagnetic material with a thickness of 100 nm was deposited by RFsputtering using SiC as a target at an Ar flow rate of 75 sccm and an O₂flow rate of 5 sccm (mixing ratio of oxygen: 6.3%). The nonmagneticmaterial was etched back with an ECR ion gun from the perpendiculardirection using a mixed gas of Ar and O₂ as a process gas at a microwavepower of 800 W and an acceleration voltage of 700V for about 12 minutes.The maximum depth of the recesses on the surface of the DTR medium was 4nm.

Comparative Example 5

A DTR medium was manufactured by the same method as in Example 5, exceptthat the nonmagnetic material was etched back by 100 nm at an angle of40° with an Ar ion milling apparatus. The maximum depth of the recesseson the surface of the DTR medium was 15 nm.

The results in Example 5 and Comparative Example 5 show that etch-backfrom perpendicular direction using an ion gun is effective for surfaceflatness.

Example 6

Using a stamper having patterns of protrusions and recesses of servopatterns (preamble, address, and burst) and magnetic dots formed thereonas shown in FIG. 2, a discrete bit-type patterned medium wasmanufactured in the method shown in FIGS. 3A to 3H. The magnetic dotshave a rectangular shape of 120 nm in the cross-track direction and 25nm in a down-track direction. This medium has a recording densitycorresponding to 130 Gbpsi. In the step of FIG. 3F, a nonmagneticmaterial was deposited by DC sputtering using a SiC—C target.Specifically, the Ar flow rate was set to 80 sccm and the depositiontime was set to 260 seconds, and a SiC—C film with a thickness of 100 nmwas deposited. In the step of FIG. 3G, the nonmagnetic material wasetched back with an ECR ion gun. The nonmagnetic material was etchedback using a mixed gas of Ar and O₂ at a microwave power of 800 W and anacceleration voltage of 700V for about 12 minutes.

As a result of acoustic emission (AE) measurement using a glide head, noAE signal was observed. As a result of AES depth profile measurement, nooxide layer was detected.

The same effects as in the DTR media in Examples 1 to 5 may be alsoexpected in the discrete bit-type patterned medium.

As hitherto described, by using processes of depositing a nonmagneticmaterial and then etching-back the nonmagnetic material using anoxygen-containing gas, the present invention can provide a patternedmedium having good surface flatness with small thickness dispersion andhigh impact resistance.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the inventions. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the inventions. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the inventions.

What is claimed is:
 1. A magnetic recording medium comprising: protrudedmagnetic patterns formed on a substrate; and a nonmagnetic materialfilled in recesses between the magnetic patterns, wherein thenonmagnetic material consists of oxygen and a material selected from thegroup consisting of Si, SiC, SiC—C, SiOC, SiON, Si₃N₄, Al, Al_(x)O_(y),Ti, and TiO_(x), and an oxygen concentration of the nonmagnetic materialis higher at a surface side than at a substrate side.
 2. The magneticrecording medium of claim 1, wherein a plurality of layers of thenonmagnetic material having an oxygen concentration being higher at thesurface side than at the substrate side are filled in the recessesbetween the magnetic patterns.